Savants might classify in the category as well.<quoted text>
Very inaccurate, there are many people who never need a dictionary. There are learning mechanisms and logic types that you have never even ones considered viable because they all differ from you.
Did you know that sociopaths actually just think differently than you? They lack the chemical reactions that produce the erratic and often detrimental emotions in their brains. Due to this all resources are utilized for learning, and they rarely need a dictionary because they become natural sponges for information. If we utilized these people more we could be on Mars already, instead of fearing them, another often irrational emotional response.
Many autistic people rarely need dictionaries either, they often become masters of using words and using even the least known definitions of words. Often twisting the meaning of what people say to suit their own ends, by utilizing obscure and lesser known meanings of the words to make what you say mean something completely different. They are also literalists, it's part of their logic method, everything is as it is, slang often escapes them, memes are a complete mystery to them.
Those are just the two of the top of my head. Two examples of people who don't need dictionaries.
(Savant syndrome is a rare, but extraordinary, condition in which persons with serious mental disabilities, including autistic disorder, have some ‘island of genius’ which stands in marked, incongruous contrast to overall handicap. As many as one in 10 persons with autistic disorder have such remarkable abilities in varying degrees, although savant syndrome occurs in other developmental disabilities or in other types of central nervous system injury or disease as well. Whatever the particular savant skill, it is always linked to massive memory.)
The savant syndrome: an extraordinary condition. A synopsis: past, present, future.
Darold A. Treffert Philos Trans R Soc Lond B Biol Sci. 2009 May 27; 364(1522): 1351–1357. doi:10.1098/rstb.2008.0326
PMC2677584.National Center for Biotechnology Information, U.S. National Library of Medicine.